The aim of this project is to study the lineage relationship between hemopoietic cells and endothelial cells in developing zebrafish. Various approaches will be used. 1) Lineage analysis, by injecting lineage tracers into single cells and looking at clones. The zebrafish is a good system with which to do this because clones can be followed in living embryos. 2) Use of the cloche mutant, in which both blood cells and hemopoietic cells are defective. Groups of cells from homozygous cloche embryos will be transplanted into wild type embryos at the blastula stages. If the mutant is cell-autonomous, there will be no labeled blood cells. If the mutation affects cells that induce blood to form, there will be. The reciprocal experiment is also planned. Although this is an interesting experiment, I do not think it answers the questions posed. The author interprets the possible results in terms of possible induction of blood by endothelial cells. However, in the transplant experiment, it could be any cell type that induces the blood cells to form. The only thing that the experiment will tell us is whether or not the cloches mutation is cell-autonomous. 3) flk1 is expressed in the endothelial cells, whilst gata 1 is expressed in the same cells in the early embryo. However, it is not clear whether this tells us that such a cell would be a common precurser without lineage analysis. 4) The aim is to isolate a zebrafish homologue of the mouse gene HEX. This is apparently expressed before flk1 in cells that appear in mouse to give rise to both blood cells and endothelial cells. The applicants will look for zebrafish HEX expression relative to flk1 and gata 1.